1. Technical Field
The invention relates to an optical coherence tomography apparatus which measures an object to be examined through the use of optical interference between measurement and reference lights.
2. Background Art
A first example of optical coherence tomography apparatuses which measures an object to be examined through the use of optical interference between measurement and reference lights is a two-beam optical coherence tomography apparatus wherein a measurement light is split into a plurality of beams (see Patent Documents 1 and 2).
According to the apparatus, the measurement light is split into two different beams, and a first composite light obtained by combining a reflected light of the first beam from an object to be examined with a reference light is received by a first spectrometer and a second composite light obtained by combining a reflected light of the second beam from the object to be examined with the reference light is received by a second spectrometer. Then, signals respectively output from the spectrometers are processed to obtain a first tomographic image formed by the first beam and a second tomographic image formed by the second beam.
The technical complexity of the apparatus, wherein two spectrometers are provided and the light is split into two fluxes by polarization, is desirably to be improved for practical use.
A known OCT apparatus is Fourier domain OCT wherein a spectral signal, in which interference signals of different wavelengths are combined, is obtained.
A second example of the apparatus is a polarization sensitive OCT (PS-OCT) which is designed to measure polarization properties of an object to be examined (see Non-Patent Document 1). The apparatus disclosed in Non-Patent Document 1 includes: an EO modulator (polarization modulator, electro-optic modulator) to scan and sequentially modulate at the same time a polarization states of beam emitted from a light source in a transverse direction of the measurement light; and two light detectors to measure at once vertical polarization components and horizontal polarization components included in spectral components. The apparatus thus structurally characterized obtains the polarization properties based on the spectral component including the vertical polarization component and the horizontal polarization component in a first polarization state of the beam and the spectral component including the vertical polarization component and the horizontal polarization component in a second polarization state of the beam.
To obtain a plurality of tomographic images of a site to be photographed, the conventional OCT was required to extract a plurality of tomographic images from tomographic images sequentially obtained at a given frame rate or have a plurality of detection systems.
In the conventional polarization sensitive OCT, it was necessary to sequentially change the beam polarization states to obtain the polarization properties using Jones vector parameters. The EO modulator used to change the polarization states is an expensive device, which is a reason why the PS-OCT is still commercially unavailable.